Motor nerves exert "trophic" influences on skeletal muscle. Recent evidence indicates that these influences are mediated in part by putative trophic substances transported by axonal flow. Our laboratory has purified a biologically-active protein from chicken sciatic nerves which exerts trophic influences on cultured muscle. This protein, referred to as sciatin, is a glycoprotein exclusively localized in the motor nerves of chickens. Immunoprecipitation studies have demonstrated that sciatin is required for that initial differentiation and subsequent maintenance of aneural chick muscle cells in vitro. Preliminary studies have suggested that sciatin is transported by axonal flow in chicken sciatic nerves and is released from chicken nerve-muscle preparations by neural stimulation. The overall objective of the proposed project is to identify a trophic substance released from the motor nerve and study its physiological functions in vivo. We are now capable of quantifying sciatin selectively, and of ascertaining its synthesis, mode of transport and mechanism of action in vivo and in vitro. This application outlines experiments which are designed to: (a) characterize sciatin by analytical procedures, (b) establish an arbitrary biological unit for sciatin, (c) produce antibodies in various animals and develop sensitive immunoassays for antibody titer, (d) develop sensitive quantitative immunoassays (ELISA) for sciatin, (e) quantitate the tissue distribution of sciatin in chickens, (f) study the immunocytochemical localization of sciatin at the electron microscopic level in chicken neural tissues (g) study the synthesis, axonal transport and release of sciatin in chicken neural tissues, (h) investigate putative sciatin receptors in muscle plasma membranes, and (i) produce monoclonal antibodies to sciatin. Successful outcome of this project will hopefully provide definitive evidence for the existence of a trophic substance released from the motor nerve. The long-term objective of the project is to further our knowledge of the trophic functions of motor neurons and thereby facilitate future study of certain muscle diseases such as muscular atrophy and muscular dytrophy whose pathogenesis may well result from disruption on normal nerve-muscle trophic interactions.